Method for optimizing fluid flow across a sample within an electron microscope sample holder

ABSTRACT

A flow directing gasket for improving the flow of a gas or liquid across electron beam transparent membranes in environmental cells within a sample holder of an electron microscope, and uses of the sample holders comprising said flow directing gaskets.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 U.S.C. §111(a) andclaims priority to U.S. Provisional Patent Application No. 62/007,162filed on Jun. 3, 2014 in the name of Daniel Stephen Gardiner andentitled “Method for Optimizing Fluid Flow Across a Sample Within anElectron Microscope Sample Holder,” which is hereby incorporated byreference herein in its entirety.

FIELD

The invention relates generally to a method for improving the flow of agas or liquid across the electron beam transparent membranes within asample holder for an electron microscope, e.g., a transmission electronmicroscope (TEM), a scanning transmission electron microscopy (STEM) andvariations of the scanning electron microscopes (SEM) that usetraditional TEM-type holders and stages, for imaging and analysis.

BACKGROUND

The sample holder is a component of an electron microscope providing thephysical support for samples under observation. To use the sampleholder, one or more samples are first placed on a sample support device.The sample support device is then mechanically fixed in place at thespecimen tip, and the sample holder is inserted into the electronmicroscope through a load-lock. During insertion, the sample holder ispushed into the electron microscope until it stops, which results in thespecimen tip of the sample holder being located in the column of themicroscope. To maintain an ultra-high vacuum environment inside theelectron microscope, flexible o-rings are typically found along thebarrel of the sample holder, and these o-rings seal against themicroscope when the sample holder is inserted.

Certain sample holders can be used to provide a means for gas or liquidto flow into and out of a cavity at the tip of the holder (see, forexample FIGS. 1 and 2). These sample holders include devices, e.g.,semiconductor devices, which are designed with relatively thin electronbeam transparent membranes, positioned in the cavity at the tip of theholder. To establish temporary or continuous flow of liquid or gas, apump located external to the sample holder can be used to force liquidsinto the cavity at the tip of the holder, including between two MEMSdevices which define an environmental cell. Since the pumping equipmentis outside of the holder, various connectors are used to bring theliquid to the sample holder, down the length of the holder, to thecavity at the tip of the holder, and back out of the sample holder. Useof a pump to flow the liquid is typical, but any method of creating apressure differential could be used to establish flow. For example, apressurized reservoir on the entry port or a depressurized reservoir onthe exit port(s) would also establish flow.

One type of sample support device is an environmental cell whichcomprises two semiconductor devices, i.e., MEMS devices, comprising thinmembrane windows and samples positioned between the semiconductordevices, wherein the sample's environment, including an electrical fieldand a gas or liquid flow, can be precisely controlled. The presentinventors previously described novel apparatuses and methods to contactand align devices used to form liquid or gas cells in InternationalPatent Application No. PCT/US2011/46282 filed on Aug. 2, 2011 entitled“ELECTRON MICROSCOPE SAMPLE HOLDER FOR FORMING A GAS OR LIQUID CELL WITHTWO SEMICONDUCTOR DEVICES,” which is hereby incorporated herein in itsentirety.

There are many reasons why environmental cell users desire liquid toflow either intermittently or continuously: flow provides a means tokeep the sample hydrated; flow allows the user to create a reaction thatcan be viewed in the microscope real time; and a system that includes atleast three ports allows users to combine two or more fluids within thecavity at the tip of the holder.

The environmental cells are typically designed such that the twosemiconductor devices are substantially parallel to one another andpositioned about 50 nm to about 5 μm relative to one another. Thisensures small liquid layers therebetween, which maximizes the microscoperesolution of the sample, which becomes less resolute as the electronbeam of the microscope travels through greater thicknesses of liquid.That said, the typical design of the environmental cells allow muchgreater volumes of fluid to flow around the semiconductor devices thanacross them. For example, in the case of a 150 nm environmental cellthickness on a Protochips Poseidon 200 holder, there is approximately500 times more cross sectional area around the E-chip than across themembrane. This creates difficulties for the users of environmental flowcells:

1.) The electron beam can create heat that can evaporate the liquid inthe cell. In many cases, greater flow across the semiconductor devicesis needed to replace the volume of gas created by electron beam heating.Increasing the flow rate into the tip of the cell can help, but itbrings higher risk of over pressurizing the cavity, potentially causingdamage;2.) Sometimes it is difficult to prepare and/or maintain the desiredsurface energy of the semiconductor devices. For example, if a surfaceis hydrophobic, it can be difficult to establish the fluid environmentdesired for a given experiment.3.) Flow rates are typically adjusted by the user with an external pumpsystem to attain the desired flow rate for sample imaging. If themajority of liquid flows around the sample area than across it, the flowrates may need to be as high as 150 microliters per hour or even higher.With a design where there is less fluid bypassing the membranes, theflow rate can be decreased. This reduction in flow rate improves safetyof the microscope, e.g., in the event of a membrane break, less fluidwill be able to escape into the column of the microscope.4.) Users that want to combine known quantities of two liquids betweenthe semiconductor devices are not able to quantify the ratio of the twofluids at the viewing area, i.e., the membranes of the semiconductordevices. This is because it is not possible to know how much liquid ofone fluid bypasses the semiconductor devices as compared to the secondfluid. This is due to asymmetry in the tip of the sample holder duringassembly;5.) In some cases, the research benefits from knowing the actual rate offluid flow. This is especially important for those studying reactions;and6.) Electrochemistry reactions can require rapid replenishment of theelectrolyte liquid to prevent the membrane area from becoming dry.

Accordingly, a fluidic cell that can overcome evaporation effects andprovide a known flow volume at of fluid at safe pressures across thesample is needed. Towards that end, an invention is disclosed herein todeliver quantifiable amounts of liquid to the membrane of anenvironmental holder.

SUMMARY

The present invention generally relates to sample holders comprisingflow directing gaskets so that fluid can be directed between MEMS chipsin environment cells, and uses of the sample holders comprising saidflow directing gaskets.

In one aspect, a flow directing gasket is described, said flow directinggasket comprising:

a first gasket having a first enclosed area, wherein the first gasketforms a seal on a first substantially planar surface;

a second gasket having a second enclosed area, wherein the second gasketforms a seal on a second substantially planar surface;

wherein the second enclosed area is smaller than the first enclosedarea; and

at least one arm member that is attached to both the first and secondgaskets, wherein the second gasket is on a plane that is different fromthat of the first gasket.

In another aspect, a sample holder for an electron microscope isdescribed, said sample holder comprising a sample holder body, a sampleholder cover, and a flow directing gasket, wherein said flow directinggasket comprises:

a first gasket having a first enclosed area, wherein the first gasketforms a seal on a first substantially planar surface;

a second gasket having a second enclosed area, wherein the second gasketforms a seal on a second substantially planar surface;

wherein the second enclosed area is smaller than the first enclosedarea; and

at least one arm member that is attached to both the first and secondgaskets, wherein the second gasket is on a plane that is different fromthat of the first gasket.

In still another aspect, a method of imaging a sample in a liquid and/orgaseous environment in an electron microscope is described, said methodcomprising inserting a sample in a sample holder, inserting the sampleholder comprising the sample in an electron microscope, introducing aliquid and/or gas to the sample in the sample holder, and imaging thesample in the electron microscope, wherein the sample holder comprises asample holder body, a sample holder cover, and a flow directing gasket,wherein said flow directing gasket comprises:

a first gasket having a first enclosed area, wherein the first gasketforms a seal on a first substantially planar surface;

a second gasket having a second enclosed area, wherein the second gasketforms a seal on a second substantially planar surface;

wherein the second enclosed area is smaller than the first enclosedarea; and

at least one arm member that is attached to both the first and secondgaskets, wherein the second gasket is on a plane that is different fromthat of the first gasket.

Other aspects, features and embodiments of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a typical electron microscope sample holder havingtwo ports for gas or liquid to flow into and out of a cavity at the tipof the holder.

FIG. 2 illustrates another embodiment of a typical electron microscopesample holder having three ports for gas or liquid to flow into and outof a cavity at the tip of the holder.

FIG. 3a is a plan view of an embodiment of the closed sample holder cellwith the sample holder cover on.

FIG. 3b is a plan view of the sample holder cell of FIG. 3a with thesample holder cover off

FIG. 3c is a plan view of the sample holder cell of FIG. 3b with thelarge MEMS chip removed.

FIG. 3d is a plan view of the sample holder cell of FIG. 3c with thesmall MEMS chip removed.

FIG. 4a is a plan view of the fluidic cavity within the two-port closedcell showing the large and small O-rings, the two ports, and the largeand small MEMS chip pockets.

FIG. 4b is a plan view of the closed cell with small MEMS chip (dotted)positioned in the cell over the small O-ring with the fluid, e.g.,liquid or gas, beginning to flow into the cell from port 1.

FIG. 4c is a plan view of the closed cell where the fluid has filled thecavity and exits the cavity via port 2.

FIG. 5a is a plan view of the fluidic cavity within the three-portclosed cell showing the large and small O-rings, the three ports, andthe large and small MEMS chip pockets.

FIG. 5b is a plan view of the closed cell with small MEMS chip (dotted)positioned in the cell over the small O-ring with the fluid, e.g.,liquid or gas, beginning to flow into the cell from ports 1 and 2.

FIG. 5c is a plan view of the closed cell where the fluid has filled thecavity and exits the cavity via port 3.

FIG. 6a illustrates the fluid flow path within a two port cell.

FIG. 6b illustrates the fluid flow path within a three port cell.

FIG. 7a is a plan view of a two port cell.

FIG. 7b illustrates the cross-section of the cell of FIG. 7a , whereFIG. 7b corresponds to the cell without fluid.

FIG. 7c illustrates the cross-section of the cell of FIG. 7a , whereFIG. 7c is the cell with fluid flowing through it.

FIG. 8a is a plan view of a three port cell.

FIG. 8b illustrates the cross-section of the cell of FIG. 8a , whereFIG. 8b corresponds to the cell without fluid.

FIG. 8c illustrates the cross-section of the cell of FIG. 8a , whereFIG. 8c is the cell with fluid flowing through it.

FIG. 9a is a plan view of the fluidic cavity within the two-port closedcell showing a flow-directing gasket, the two ports, and the large andsmall MEMS chip pockets.

FIG. 9b is a plan view of the closed cell with small MEMS chip (dotted)positioned in the cell over the small gasket of the flow-directinggasket with the fluid, e.g., liquid or gas, beginning to flow into thecell from port 1.

FIG. 9c is a plan view of the closed cell where the fluid has filled thecavity and exits the cavity via port 2.

FIG. 10a is a plan view of the fluidic cavity within the three-portclosed cell showing a flow-directing gasket, the three ports, and thelarge and small MEMS chip pockets.

FIG. 10b is a plan view of the closed cell with small MEMS chip (dotted)positioned in the cell over the small gasket of the flow-directinggasket with the fluid, e.g., liquid or gas, beginning to flow into thecell from ports 1 and 2.

FIG. 10c is a plan view of the closed cell where the fluid has filledthe cavity and exits the cavity via port 3.

FIG. 11a illustrates the fluid flow path within a two port cell, whereinthe two port cell includes the flow-directing gasket.

FIG. 11b illustrates the fluid flow path within a three port cell,wherein the two port cell includes the flow-directing gasket.

FIG. 12a is a plan view of a two port cell without the cover on or thelarge MEMS chip.

FIG. 12b illustrates the cross-section of the cell of FIG. 12a , whereFIG. 12b corresponds to the cell without fluid.

FIG. 12c illustrates the cross-section of the cell of FIG. 12a , whereFIG. 12c is the cell with fluid flowing through it.

FIG. 13a is a plan view of a three port cell without the cover on or thelarge MEMS chip.

FIG. 13b illustrates the cross-section of the cell of FIG. 13a , whereFIG. 13b corresponds to the cell without fluid.

FIG. 13c illustrates the cross-section of the cell of FIG. 13a , whereFIG. 13c is the cell with fluid flowing through it.

FIG. 14a illustrates the two port sample holder with the flow directinggasket as well as how the gasket and the MEMS chips are loaded into thesample holder.

FIG. 14b is an exploded view of the sample holder with the flowdirecting gasket.

FIG. 15a illustrates the sample holder without a gasket of MEMS chips.

FIG. 15b illustrates the placement of the flow directing gasket in theFIG. 15a sample holder.

FIG. 15c illustrates the placement of the small MEMS chip in the FIG.15b sample holder.

FIG. 15d illustrates the placement of the large MEMS chip in the FIG.15c sample holder.

FIG. 15e illustrates the placement of the cover on the FIG. 15d sampleholder. FIG. 15f illustrates the affixation of the cover.

FIG. 16a illustrates the three port sample holder with the flowdirecting gasket as well as how the gasket and the MEMS chips are loadedinto the sample holder.

FIG. 16b illustrates another embodiment of the three port sample holderwith the flow directing gasket as well as how the gasket and the MEMSchips are loaded into the sample holder.

FIG. 16c illustrates the positioning of the gasket in the sample holderof FIG. 16 a.

FIG. 16d illustrates the positioning of the gasket in the sample holderof FIG. 16 b.

FIG. 16e illustrates the 3-dimensional image of the alternative flowdirecting gasket.

FIG. 17 illustrates alternative gasket shapes.

FIG. 18 illustrates the minimum number of arm members needed for a2-port and a 3-port sample holder.

FIG. 19 illustrates another embodiment of the flow directing gaskethaving braces for securing the large MEMS device.

DETAILED DESCRIPTION

The present invention generally relates to sample holders comprisingflow directing gaskets so that fluid can be directed between MEMS chipsin environment cells, and uses of the sample holders comprising saidflow directing gaskets. It is to be understood that the sample holderand sample holder interface described herein are compatible with and maybe interfaced with the sample support devices, e.g., semiconductorsample support devices, disclosed in International Patent ApplicationNos. PCT/US08/63200 filed on May 9, 2008, PCT/US11/46282 filed on Aug.2, 2011, and PCT/US08/88052 filed on Dec. 22, 2008, which are allincorporated herein by reference in their entireties. It should also beappreciated by one skilled in the art that alternative sample supportdevices may be interfaced with the sample holder described herein. Thesample holder provides mechanical support for one or more samples orsample support devices and also provides other stimuli (e.g.,temperature, electricity, mechanical, chemical, gas or liquid, or anycombination thereof) to the samples or sample support devices. Thesample holder can be manufactured with tips, barrels and ends of variousshapes and sizes such that the sample holder fits any manufacturer'selectron microscope.

As used herein, a “sample support device” corresponds to a structurethat holds a sample for microscopic imaging. A sample support device canprovide an experimental region. Devices may include one, more than oneor even an array of experimental regions and may include integratedfeatures such as electrodes, thermocouples, and/or calibration sites, asreadily determined by one skilled in the art. One preferred embodimentincludes sample support devices made with MEMS technology and with thinmembranes (continuous or perforated) for supporting a sample in theexperimental region. Sample support devices include, but are not limitedto, a window device, an electrical device and a heating device.

As defined herein, a “membrane region” on the sample support devicecorresponds to unsupported material comprising, consisting of, orconsisting essentially of carbon, silicon nitride, SiC or other thinfilms generally 1 micron or less having a low tensile stress (<500 MPa),and providing a region at least partially electron transparent regionfor supporting the at least one sample. The membrane region may includeholes or be hole-free. The membrane region may be comprised of a singlematerial or a layer of more than one material and may be eitheruniformly flat or contain regions with varying thicknesses.

The general area of “in situ” electron microscopy involves applyingstimulus to a sample during imaging. The stimulus could be thermal(heating or cooling), electrical (applying a voltage or current),mechanical (applying stress or strain), chemical (containing a sample ina specific chemical environment), or several of these at once.

As defined herein, a “cell” corresponds to a region defined by twosubstantially parallel positioned devices, wherein at least one liquidand/or gas can be flowed therethrough. A sample can be positioned withinthe cell for imaging purposes.

As defined herein, “sample” means the object being studied in theelectron microscope, typically placed within or on the device in theregion of liquid or gas control which is at least partially electrontransparent (e.g., nanoparticle, catalyst, thin section, etc.).

As defined herein, a “pocket” corresponds to a space in the sampleholder that defines the vertical walls of the cell, into which the twosubstantially parallel devices are positioned to form the cell.

As defined herein, “window device” means a device used to create aphysical, electron transparent barrier on one boundary and the vacuumenvironment of the electron microscope on the other and is generally asilicon nitride-based semiconductor micro-machined part, although othersemiconductor materials are contemplated.

As defined herein, an “arm member” corresponds to a portion of thegasket that connects the outer gasket (i.e., the first gasket) to theinner gasket (i.e., the second gasket) and ensures that the fluids flowbetween two MEMS chips and to provide a known flow volume at of fluid atsafe pressures across the sample. Further, the arm member can provide aholding force to the MEMS device.

FIGS. 1 and 2 show a general depiction of a two port closed cell holderand a three port closed cell holder, respectively, wherein the sampleholder includes tubing inside the electron microscope (EM) holder thattravels to and from the closed cell at the specimen tip. The placementof the tubing is just for general illustration and is not intended tolimit the holder in any way. The tubing permits fluids, e.g., gases orliquids, to travel to the closed cell, for in situ analysis of thesample positioned in the closed cell.

FIGS. 3a-3d illustrate an example of the closed cell that is positionedat the specimen tip. The closed cell in FIGS. 3a-3d is just for generalillustration and is not intended to limit the closed cell in any way.FIG. 3a is a plan view of the closed cell, wherein a cover of the closedcell is shown positioned and affixed, e.g., with screws, to the cell.FIG. 3b is a plan view of the closed cell with the cover off, revealingthe first of two MEMS chips (i.e., a sample support device) positionedin the cell. FIG. 3c is a plan view of the closed cell showing thesecond of two MEMS chips after the first MEMS chip is removed. The largeand small MEMS chips are stacked on top of one another and the sample“sandwiched” between the two chips. FIG. 3c also reveals the first oftwo O-rings, which is positioned below the large MEMS chip (e.g., athermal or electrical device) to seal the cell so liquid or gas can beintroduced into the cell. FIG. 3d is a plan view of the closed cellshowing the bottom of the cell after the second MEMS chip (e.g., awindow device) is removed. FIG. 3d also reveals the second of twoO-rings, which is positioned below the small MEMS chip to form thesecond seal so liquid or gas can be introduced into the cell. Thefluidic reservoir in FIG. 3d corresponds to the area between the twoO-rings when the MEMS chips are in place. Although not illustrated inFIGS. 3a-3d per se, the fluidic reservoir indicated in FIG. 3d has depthto accommodate the MEMS chips. It should be appreciated that the “closedcell” remains in fluid communication with fluidic inlets and hence theclosed cell receives fluids from an external source and fluids arereturned from the closed cell to an external source. Further, the closedcell has a pocket(s) that can include contact points, or protrusions,rather than straight edge walls so as to improve alignment of thedevices in the cell holders. Further, in FIGS. 3a -3 d, as well as everyother sample holder described herein, the holder can have grooves thataccept the gasket to fix the gasket position in the sample holder.

FIGS. 4a-4c illustrates the fluidic cavity within a two port closed cellthat is positioned at the specimen tip. The closed cell in FIGS. 4a -4c, which does not illustrate the cover nor the large MEMS chip, is justfor general illustration and is not intended to limit the closed cell inany way. FIG. 4a is a plan view of the fluidic cavity within thetwo-port closed cell showing the large and small O-rings, the two ports,and the large and small MEMS chip pockets. It should be appreciated thatthe chip pockets can include the aforementioned protrusions, which arenot shown in FIGS. 4a -4 c. FIG. 4b is a plan view of the closed cellwith small MEMS chip (dotted) positioned in the cell over the smallO-ring with the fluid, e.g., liquid or gas, beginning to flow into thecell from port 1. FIG. 4c is a plan view of the closed cell where thefluid has filled the cavity and exits the cavity via port 2. Althoughnot shown, in order to fill the cavity as depicted in FIG. 4c , thelarge MEMS chip has to be in place in the larger pocket covering thelarge O-ring. The large MEMS chip is not shown so that the filled cavitycan be envisioned.

FIGS. 5a-5c illustrates the fluidic cavity within a three port closedcell that is positioned at the specimen tip. The closed cell in FIGS. 5a-5 c, which does not illustrate the cover nor the large MEMS chip, isjust for general illustration and is not intended to limit the closedcell in any way. FIG. 5a is a plan view of the fluidic cavity within thethree-port closed cell showing the large and small O-rings, the threeports, and the large and small MEMS chip pockets. It should beappreciated that the chip pockets can include the aforementionedprotrusions, which are not shown in FIGS. 5a -5 c. FIG. 5b is a planview of the closed cell with small MEMS chip (dotted) positioned in thecell over the small O-ring with the fluid, e.g., liquid or gas,beginning to flow into the cell from ports 1 and 2. FIG. 5c is a planview of the closed cell where the fluid has filled the cavity and exitsthe cavity via port 3. Although not shown, in order to fill the cavityas depicted in FIG. 5c , the large MEMS chip has to be in place in thelarger pocket covering the large O-ring. The large MEMS chip is notshown so that the filled cavity can be envisioned.

FIG. 6a illustrates the fluid flow path within a two port cell.Specifically, in a typical two port design, the fluid tends to flowaround the small MEMS chip from port 1 to port 2. FIG. 6b illustratesthe fluid flow path within a three port cell. Specifically, in a typicalthree port design, the fluid tends to flow around the small MEMS chipfrom ports 1 and 2 to port 3. Either way, the fluid will have higherflow rates where there is least resistance, which happens to be aroundthe MEMS devices rather than across the membrane interface.

FIG. 7 illustrates the cross section of a two port cell. For example,FIGS. 7b and 7c illustrate the cross-section of the cell of FIG. 7a ,where FIG. 7a is a plan view of a two port cell. FIG. 7b corresponds tothe cell without fluid while FIG. 7c is the cell with fluid flowingthrough it. The purpose of FIG. 7 is to illustrate the gaps where thereis less resistance to flow around the MEMS chips than the small gapsbetween the MEMS chips. The liquid flow will be higher in gaps of largercross sectional area than those with small cross sectional area.Although not shown, the sample is positioned in the small gap betweenthe MEMS chips.

FIG. 8 illustrates the cross section of a three port cell. For example,FIGS. 8b and 8c illustrate the cross-section of the cell of FIG. 8a ,where FIG. 8a is a plan view of a three port cell. FIG. 8b correspondsto the cell without fluid while FIG. 8c is the cell with fluid flowingthrough it. The purpose of FIG. 8 is to illustrate the gaps where thereis less resistance to flow around the MEMS chips than the small gapsbetween the MEMS chips. The liquid flow will be higher in gaps of largercross sectional area than those with small cross sectional area.Although not shown, the sample is positioned in the small gap betweenthe MEMS chips.

FIGS. 1 through 8 display a typical closed cell environmental cellholder of the prior art. Disadvantageously, due to the very small gapsbetween the membranes of the MEMS devices, fluid dynamics dictate anaffinity for the majority of the fluid to bypass the membranes. In orderto overcome this shortcoming, the option available to the user isincreasing the flow rates through the cell, which will increase thepressure within the cell, creating a potential for leaks or otheradverse affects.

FIGS. 9a-9c illustrates the fluidic cavity within a two port closed cellof the present invention. The closed cell in FIGS. 9a -9 c, which doesnot illustrate the cover nor the large MEMS chip, is just for generalillustration and is not intended to limit the closed cell in any way.FIG. 9a is a plan view of the fluidic cavity within the two-port closedcell showing a flow-directing gasket, the two ports, and the large andsmall MEMS chip pockets. The gasket can be made from typical elastomericmaterials including, but not limited to, perfluoroelastomers,fluoroelastomers, and EPDM. Since the gasket is disposable, the user cansimply select a material that is chemically compatible for theirexperiment. Although shown as one monolithic piece, it should beappreciated by the person skilled in the art that the gasket cancomprise multiple pieces that can be put together to make the gasket. Itshould be appreciated that the chip pockets can include theaforementioned protrusions, which are not shown in FIGS. 9a-9c . FIG. 9bis a plan view of the closed cell with small MEMS chip (dotted)positioned in the cell over the small gasket of the flow-directinggasket with the fluid, e.g., liquid or gas, beginning to flow into thecell from port 1. FIG. 9c is a plan view of the closed cell where thefluid has filled the cavity and exits the cavity via port 2. Althoughnot shown, in order to fill the cavity as depicted in FIG. 9c , thelarge MEMS chip has to be in place in the larger pocket covering thelarge gasket of the flow directing gasket. The large MEMS chip is notshown so that the filled cavity can be envisioned.

The flow directing gasket of FIGS. 9a-9c comprises generally a firstgasket having a first two-dimensional shape having a first enclosedarea; a second gasket having a second two-dimensional shape having asecond enclosed area, wherein the second enclosed area is smaller thanthe first enclosed area; and at least one arm member that is attached toboth the first and second gaskets, wherein the second gasket is on aplane that is different from that of the first gasket. Alternatively,the flow directing gasket of FIGS. 9a-9c comprises a first gasket havinga first enclosed area, wherein the first gasket forms a seal on a firstsubstantially planar surface; a second gasket having a second enclosedarea, wherein the second gasket forms a seal on a second substantiallyplanar surface; wherein the second enclosed area is smaller than thefirst enclosed area; and at least one arm member that is attached toboth the first and second gaskets, wherein the second gasket is on aplane that is different from that of the first gasket. In either case,the first enclosed area can be circular or square or rectangular, andthe second enclosed area can be circular or square or rectangular,wherein the shape of the first enclosed area and the second enclosedarea can be the same as or different from one another, and wherein thesecond enclosed area is smaller than the first enclosed area. The firstsubstantially planar surface corresponds to a surface of a larger MEMSdevice (see, for example, FIGS. 12b, 12c, 13b, and 13c ) and the secondsubstantially planar surface corresponds to a surface of the smallerMEMS device (see, for example, FIGS. 12b, 12c, 13b, and 13c ). It shouldbe appreciated that “substantially planar” is intended to capturesurfaces (e.g., MEMS devices) that have irregularities on the surfacebut are ostensibly planar since the production of a perfectly planarsurface is not always possible.

FIGS. 10a-10c illustrates the fluidic cavity within a three port closedcell of the present invention. The closed cell in FIGS. 10a -10 c, whichdoes not illustrate the cover nor the large MEMS chip, is just forgeneral illustration and is not intended to limit the closed cell in anyway. FIG. 10a is a plan view of the fluidic cavity within the three-portclosed cell showing a flow-directing gasket, the three ports, and thelarge and small MEMS chip pockets. It should be appreciated that thechip pockets can include the aforementioned protrusions, which are notshown in FIGS. 10a -10 c. FIG. 10b is a plan view of the closed cellwith small MEMS chip (dotted) positioned in the cell over the smallgasket of the flow-directing gasket with the fluid, e.g., liquid or gas,beginning to flow into the cell from ports 1 and 2. FIG. 10c is a planview of the closed cell where the fluid has filled the cavity and exitsthe cavity via port 3. Although not shown, in order to fill the cavityas depicted in FIG. 10c , the large MEMS chip has to be in place in thelarger pocket covering the large gasket of the flow directing gasket.The large MEMS chip is not shown so that the filled cavity can beenvisioned.

FIG. 11a illustrates the fluid flow path within a two port celldescribed herein, wherein the two port cell includes the flow-directinggasket. In the two port design, the fluid must flow across the interfaceof the MEMS chips from port 1 to port 2, as depicted by the arrow fromport 1 to port 2. The elastomeric gaskets create a seal that wouldotherwise be a gap between the MEMS chips and the supporting structure.FIG. 11b illustrates the fluid flow path within a three port celldescribed herein, wherein the two port cell includes the flow-directinggasket. Similar to the two-port design, in the three port design, thefluid must flow across the interface of the MEMS chips from ports 1 and2 to port 3, as depicted by the arrows in FIG. 11 b.

FIG. 12 illustrates the cross section of a two port cell describedherein. For example, FIGS. 12b and 12c illustrate the cross-section ofthe cell of FIG. 12a , where FIG. 12a is a plan view of a two port cellwithout the cover on or the large MEMS chip. FIG. 12b corresponds to thecell without fluid while FIG. 12c is the cell with fluid flowing throughit. Of note, the cells in FIGS. 12b and 12c include the cover and thelarge MEMS chip, which were excluded from FIG. 12a for illustrativepurposes only. The purpose of FIG. 12 is to illustrate the eliminationof the gaps of FIG. 7 whereby the fluid flow is limited to the pathbetween the MEMS chips. Although not shown, the sample is positioned inthe small gap between the MEMS chips.

FIG. 13 illustrates the cross section of a three port cell describedherein. For example, FIGS. 13b and 13c illustrate the cross-section ofthe cell of FIG. 13a , where FIG. 13a is a plan view of a three portcell without the cover on or the large MEMS chip. FIG. 13b correspondsto the cell without fluid while FIG. 13c is the cell with fluid flowingthrough it. Of note, the cells in FIGS. 13b and 13c include the coverand the large MEMS chip, which were excluded from FIG. 13a forillustrative purposes only. The purpose of FIG. 13 is to illustrate theelimination of the gaps of FIG. 8 whereby the fluid flow is limited tothe path between the MEMS chips. Although not shown, the sample ispositioned in the small gap between the MEMS chips.

FIGS. 14a and 14b shows an exploded view of the sample holder with theflow directing gasket described herein as well as how the gasket and theMEMS chips are loaded into the sample holder. The flow directing gasketcan be customized based on the design of sample holder, the size andshape of the respective MEMS chips, and the sealing method (e.g.,O-rings). Of note, the flow directing gasket is shown as a single,contiguous article having two gaskets in different planes and at leastone arm member that connects the small gasket to the large gasket,wherein the at least one member maintains the two gaskets in differentplanes. In the case of the FIG. 14, four arm members are shownconnecting the small gasket to the large gasket. It should beappreciated that only one member is needed to connect the large gasketand the small gasket (see, e.g., FIG. 16). Other embodiments of the flowdirecting gasket can be easily contemplated based on the position of theports and the size and shape of the MEMS devices, as understood by theperson skilled in the art. Regardless, the flow directing gasket will becompressed when the cover is attached to the body of the sample holderso as to prevent gases or liquids from escaping from between the holderbody and the holder cover and to minimize the bypass of fluids aroundthe MEMS chips, ensuring instead that the fluids substantially flowbetween the two MEMS chips. Both features are accomplished because thegasket comprises “steps” to transition from one plane to another,wherein the step is the shape of the edge of the small MEMS chip andwherein the riser of the steps is substantially the same height as thedepth of the small MEMS chip such that upon compression, i.e., the coveraffixed to the body of the sample holder, fluids will not substantiallypass between the gasket and the edge of the MEMS chip (see, e.g., FIG.12c ). Moreover, the distance between the “step down” and the “step up”is the length of the small MEMS chip.

The cell holders and lids described herein are preferably titanium orbrass and are died to guarantee very vertical and parallel pocket edges.

FIGS. 15a -f display the loading of the flow directing gasket (FIG. 15b) and the two MEMS chips (FIGS. 15c and 15d ) in the sample holderfollowed by the placement and affixation of the cover thereon (FIGS. 15eand 15f . During loading, the sample will be positioned between themembrane of the first loaded MEMS chip (e.g., the small MEMS chip) andthe membrane of the second loaded MEMS chip (e.g., the large MEMS chip).The cover can be secured to the holder body using at least one screw(e.g., as shown in FIG. 15f or other fastening means.

FIG. 16 shows an alternative flow directing gasket design. This designhas a gasket that can be configured to either bypass the membrane or toflow across it, depending on the assembly orientation. In FIGS. 16a and16c , the gasket is positioned in a three port cell in an orientationthat allows the majority of fluid to bypass the MEMS chip membranes. InFIGS. 16b and 16d , the gasket is positioned in the three port cell inan orientation that allows the fluid to flow across the MEMS chipmembranes. FIG. 16e illustrates the 3-dimensional image of thealternative flow directing gasket.

FIG. 17 illustrates alternative gasket shapes wherein the first gaskethas a two-dimensional shape that is circular or square or rectangularand has a first enclosed area, and the second gasket has atwo-dimensional shape that is circular or square or rectangular and hasa second enclosed area, wherein the shape of the first gasket and thesecond gasket can be the same as or different from one another, andwherein the second enclosed area is smaller than the first enclosedarea. It should be appreciated by the person skilled in the art thatalternative gasket shapes to those shown are also contemplated. It canbe seen that the arm members can be positioned in a variety of places tohold the first gasket and the second gasket together. In each case, thearm members serve to direct the fluid between the two MEMS chips.

FIG. 18 illustrates the minimum number of arm members needed for a2-port and a 3-port sample holder, wherein at least one arm member ispositioned between an inlet port and an outlet port.

Another advantage of the arm member is to provide a holding force to theMEMS device. This can be seen most easily in FIGS. 12c, 13c and 15c .Gripping the edge of the MEMS device allows the device to be centeredmore accurately in the assembly and also prevents the device from comingloose from it's intended placement. In other words, the electronmicroscopy sample holder comprises a gasket that creates a seal betweenthe primary planar surface of a MEMS device and a planar surface of thesample holder such that the holder has grooves that accept the perimeterof the gasket to fix the gasket position in the sample holder with armmembers attached to the gasket that extend to one or more edges of theMEMS device to fix the MEMS device position in the sample holder. Thoughthese figures show the arm members gripping the smaller of the twodevices, a similar bracing feature would have the same benefit for thelarger device (see, e.g., FIG. 19).

In practice, liquids or gases can be flowed in and out of the liquid,electrochemical or thermal environmental cells described herein throughthe supply lines without leaking to the outside environment. Electricalcurrent and voltage can be supplied to the electrical or thermal devicethrough the electrical supply lines. The holder can be placed in a TEM,the liquid, electrical or thermal device can be set to the desiredcurrent/voltage, and the type of liquid/liquids/gas/gases can be setapplied to the sample using the supply lines. During imaging, theelectron beam passes through the hole in the holder lid, strikes thesample on the heating membrane of the upper (window, thermal orelectrical) device, passes through the window on the lower (window)device, then exits the gas cell through the hole on the bottom of theholder body.

The use of multiple inputs/outputs to the sample holder provides for theintroduction of multiple reagents during use. This allows the user toimage chemicals as they mix/react in real time within the environmentalcell. It also improves time resolution since a chemical can be loaded,then released at a precise moment into the cell. For example, if a livecell is being imaged, the user can watch the live cell in flowingliquid, then introduce a fixative through a second input toinstantaneously fix the cell. Alternatively, two different liquids canbe input from either side of the liquid cell, react in the cell (betweenthe windows), then released from a third port. It should be appreciatedthat the liquid cell, thermal cell, or electrochemical cell describedherein can have one input and one output or any combination of multipleinputs/outputs as readily determined by the skilled artisan.

Accordingly, in another aspect, a method of imaging a sample in a liquidand/or gaseous environment in an electron microscope, said methodcomprising inserting a sample in a sample holder, inserting the sampleholder comprising the sample in an electron microscope, introducing aliquid and/or gas to the sample in the sample holder, and imaging thesample in the electron microscope, wherein the sample holder comprises asample holder body, a sample holder cover, and a gasket describedherein.

Although the invention has been variously disclosed herein withreference to illustrative embodiments and features, it will beappreciated that the embodiments and features described hereinabove arenot intended to limit the invention, and that other variations,modifications and other embodiments will suggest themselves to those ofordinary skill in the art, based on the disclosure herein. The inventiontherefore is to be broadly construed, as encompassing all suchvariations, modifications and alternative embodiments within the spiritand scope of the claims hereafter set forth.

What is claimed is:
 1. A flow directing gasket comprising: a firstgasket having a first enclosed area, wherein the first gasket forms aseal on a first substantially planar surface; a second gasket having asecond enclosed area, wherein the second gasket forms a seal on a secondsubstantially planar surface; wherein the second enclosed area issmaller than the first enclosed area; and at least one arm member thatis attached to both the first and second gaskets, wherein the secondgasket is on a plane that is different from that of the first gasket. 2.The gasket of claim 1, wherein the at least one arm member has a firstand a second end, wherein the first end is attached to the first gasketand second end is attached to the second gasket.
 3. The gasket of claim1, wherein the gasket comprises two arm members.
 4. The gasket of claim1, wherein the gasket comprises three arm members.
 5. The gasket ofclaim 1, wherein the gasket comprises four arm members.
 6. The gasket ofclaim 1, wherein the second gasket is substantially centered relative tothe first gasket.
 7. The gasket of claim 1, wherein the second gasket isnot substantially centered relative to the first gasket.
 8. The gasketof claim 1, wherein the at least one member comprises a step from afirst plane of the first gasket to a second plane of the second gasket.9. The gasket of claim 8, wherein the step is shaped to form a seal atthe edge of a MEMS chip such that fluid will not flow between the stepand the edge of the MEMS chip.
 10. The gasket of claim 8, wherein thestep is shaped to provide a holding force to a first MEMS device. 11.The gasket of claim 8, wherein the step comprises a riser that has aheight that is substantially similar to a depth of a MEMS chip.
 12. Thegasket of claim 1, wherein the first area defines a circle, a square ora rectangle.
 13. The gasket of claim 1, wherein the second area definesa circle, a square or a rectangle.
 14. The gasket of claim 1, whereinthe first substantially planar surface comprises a MEMS device selectedfrom the group consisting of a window device, an electrical device, anda thermal device.
 15. The gasket of claim 1, wherein the secondsubstantially planar surface comprises a MEMS device selected from thegroup consisting of a window device, an electrical device, and a thermaldevice.
 16. The gasket of claim 1, wherein the first gasket comprises atleast one brace to provide a holding force to a second MEMS device. 17.A sample holder for an electron microscope, said sample holdercomprising a sample holder body, a sample holder cover, and a gasket ofclaim
 1. 18. The sample holder of claim 17, further comprising at leastone MEMS chip.
 19. A method of imaging a sample in a liquid and/orgaseous environment in an electron microscope, said method comprisinginserting a sample in a sample holder, inserting the sample holdercomprising the sample in an electron microscope, introducing a liquidand/or gas to the sample in the sample holder, and imaging the sample inthe electron microscope, wherein the sample holder comprises a sampleholder of claim 17.